The present invention relates to a method for determining the current return path integrity in an electric device with a plurality of signal lines and supply lines, wherein said electric device is connected or connectable to a further device. In particular, the invention relates to a method for determining the current return path integrity in a connector receptacle with a plurality of signal lines and supply lines, wherein said receptacle is connected or connectable to a printed circuit board. Further the present invention relates to a test device for performing the above method.
An electric device with a plurality of signal lines and supply lines is usually connected to a further electric device. For example, said electric device may be a connector receptacle and said further electric device may be a printed circuit board. The connector receptacle is connected to the printed circuit board by a plurality of soldering joints. There are at least two types of supply lines, for example VDD lines and GND (ground) lines, where VDD stands for the positive supply voltage of an integrated circuit. If a circuit or device on the printed circuit board requires several voltages, then there are a corresponding number of different voltage lines. For example, an integrated circuit can require an additional negative voltage supply line VSS.
The supply lines, in particular the VDD and GND lines are provided for the power distribution in a printed circuit board. The supply lines of the same type are interconnected together and are therefore redundant supply lines. Each redundant supply line of the connector assembly is connected to a corresponding supply trace on the printed circuit board by a soldering joint. If there is an opening in said soldering joint, then the connection is maintained via the other supply lines of the same type. If a direct current is applied to the supply lines, then the single opening has no influence to the electric properties of the supply lines.
However, if an alternating current with a high frequency is applied to the supply lines or the signal lines, then the opening in the soldering joint causes a substantial change of the electric properties of the whole electric device. The supply lines, e.g. the VDD and GND lines are coupled capacitive and inductive to the signal lines. The supply lines are utilized as high frequency signal return paths. Losing one or more of those signal return paths causes additional impedance mismatches and an increased signal-to-signal coupling, which may be seriously impact high-speed system performance and reliability.
Therefore it is important to test high-speed signal paths after assembly as accurately as possible. In selected cases this can be done on a test bench. However, there is a serious problem, if an online assembly inspection of large connectors with more than 1000 signal connectors has to be done.
Known electric online testing methods allow the detection of signal shorts and openings as well as inter-power shorts. In the case of redundant VDD and GND connections it is very difficult to detect one or more openings by an AC (Alternating Current) and/or DC (Direct Current) resistance measurements. Additionally the location of the malicious signal return path opening has to be known to identify the affected signal traces.
Further an optical inspection, e.g. by X-ray, is manually possible in some cases. However, said optical inspection is very difficult and time consuming. The optical inspection also depends on human factors. Especially large and complex structured connector assemblies with thousands of signals require online testing methods during the manufacturing process.
There is no known method for an automatic testing to electrically localize redundant VDD and/or GND openings. Therefore the test coverage of high-speed links and interfaces is significantly exposed. This leads to data integrity and functionality problems during initial system test and thereby to increased hardware cost and system test delay.